Disc drives are data handling systems used to magnetically store and retrieve digital data files. A typical disc drive comprises a sealed housing which encloses one or more rotatable discs to which data are magnetically stored by a corresponding array of read/write transducing heads. The heads are supported by a rotatable actuator and moved to various tracks defined on the disc surfaces by an actuator motor. The discs are supported and rotated by a spindle motor at a constant high speed.
A typical disc drive housing comprises a rigid base deck having a substantially planar support area to support the various mechanical subassemblies of the drive. A top cover mates with side walls extending vertically around the perimeter of the support area to complete the enclosure. A typical housing configuration uses a relatively thick cast aluminum base deck and a relatively thin stainless steel stamped top cover.
Current disc drive designs are typically configured to accommodate a “top-down” assembly methodology in which automated assembly lines use robotic arms to sequentially assemble the various subassemblies onto each base deck. Once all of the subassemblies have been installed, a top cover is mated with and secured to the base deck using a number of external fasteners. Typically, fasteners are additionally inserted through the top cover into top portions of the spindle motor and actuator assembly.
While affixing the spindle motor and actuator assembly to both the top cover and the base deck improves the mechanical support of these subassemblies, such configuration also enhances the excitation of the housing during operation of the disc drive, undesirably resulting in the generation of acoustic noise.
The level of sound radiation from a disc drive housing through excitation of the housing is generally determined by sound energy produced by the rotating discs, and vibration energy produced by the rotating discs and by movement of the actuator assembly during access (seek) operations as the heads are quickly moved to different tracks on the disc surfaces. Generally, thicker housing structures attenuate excitation energy better than thin structures. Since the top cover is usually thinner than the base deck, the cover will tend to transmit more acoustic energy than the base deck.
In an effort to reduce the generation of acoustic noise, disc drive manufacturers have attempted to dampen the housing structure to increase attenuation (transmission loss). For example, U.S. Pat. No. 5,875,067 issued to Morris et al. discloses providing a small, circumferentially extending acoustic compliance area as a thinned area immediately surrounding a contact point to which an excitation source (spindle motor, actuator assembly) is attached. This compliance area is selected to “decouple” the excitation source from remaining portions of the housing so that excitation energy is not passed to the remaining portions of the housing. U.S. Pat. No. 5,214,549 issued to Baker et al. discloses a constrained layer damping structure formed by placing a visco-elastic layer of material on a portion of a housing surface and then placing a thin, rigid layer of material on the visco-elastic layer. This allows shear forces in the visco-elastic layer to dissipate excitation of the housing structure.
While operable, there remains a continued need for improvements in the art to reduce disc drive housing excitation to accommodate ever higher levels of disc drive performance. It is to such improvements that the present invention is directed.